In recent years, demand for portable electronic devices such as a cellular phone and a notebook computer has grown. In such electronic devices, thin portable terminals having sound functions such as a video phone, a movie play, and a hands-free phone as commodity values have being developed. In the development thereof, the requirements for a high-quality sound and a reduction in size and thickness have increased with respect to an electro-acoustic transducer (speaker) which is an acoustic component.
Presently, in electronic devices such as a cellular phone, an electro-dynamic electro-acoustic transducer has been used as an electro-acoustic transducer. The electro-dynamic electro-acoustic transducer is constituted by a permanent magnet, a voice coil, and a vibrating membrane.
However, the electro-dynamic electro-acoustic transducer has a limit to a reduction in thickness due to the operation principle and the structure thereof. On the other hand, Patent Documents 1 and 2 discloses that a piezoelectric element is used as the electro-acoustic transducer.
In addition, as another example of an oscillator making use of the piezoelectric element, in addition to a speaker, various electronic devices or oscillators such as a sound wave sensor (Patent Document 3) that detects the distance to an object using a sound wave oscillated from the piezoelectric element are known (Patent Document 4).